Expulsion lightning arrester



Oct. 5, 1943. R. R. PITTMAN EXPULSION LIGHTNNG ARRESTER Filed Sept. 22, 1941 R O T N E v N Patented Oct. 5, 1943 UNITED STATES PATENT OFFICE EXPULSION LIGHTNING ARRESTER Ralph R. Pittman, Pine Blui, Ark.

Application September 22, 1941, Serial No. 411,737

6 Claims.

This invention relates generally to lightningprotection devices, and particularly to that type of lightning arresters in Which arcing gaps are provided for the purpose of limiting the Voltage of a connected conductor to a predetermined value, and in which an arc following breakdown of the gaps is subsequently extinguished by expulsion action.

Heretofore devices of this character which embody a longitudinally extending arc space of uniform cross-sectional area bounded by gasevolving insulating material have had a limited range of .current interrupting ability determined by the length and area of the breakdown path. In order to extend the range of interrupting ability, impedances, usually resistors, have been used in series with the device, for the Ypurpose of limiting the current due to normal voltage applied to the broken-down path to some maximum value within the operating range of the device. Such impedances-have been mounted externally of the device, requiring additional series and shunting gaps also externally mounted.

It is an object of the present invention to provide a, construction in which a current-limiting impedance is embodied, and in which the discharge of the inherently conducting gas is utilized in cooperation with the electrodes normally required by the device to provide improved series and shunting characteristics which are variable in accordance with the quantity of electricity passing through the device, thereby reducing the number of parts required, as well as providing a simpler and more compact structure of greater effectiveness.

With this and other objects in view which appear from the description, my invention resides in the novel form, construction and arrangements of the parts constituting the device, and the scope ofY the invention will be indicated in the appended claims.

The invention is illustrated in the accompanying drawing, in which Fig. l is a longitudinal elevation shown principally in section, and Fig. 2 ls a section taken along the line II-II of Fig. l.

As shown in the embodiment illustrated, an outer hollow tubular insulator l0, of uniform diameter, is tted at its respective ends with the upper and lower electrodes of conducting material I2 and I3, by means of cooperating threads Von these members, the upper electrode I2 closing the upper -end of the insulator IG. The insulator I contains the hollow tubular insulator II, also of uniform diameter, the latter being secured in spaced coaxial relationship with the former by the extension of the upper end portion of the member II into the recess 3l of the upper electrode I2, and the extension of the lower end portion of the member II into the recess 38 of the lower electrode I3. The outer diameter of the insulator II is less than the inner diameter of the insulator Iii, the longitudinally extending annular space therebetween being designated by the reference character I4.

The hollow I5 of the insulator Il contains an impedance member, here shown as a wound type resistor which extends coaxially upward from the lower end of the insulator II toward and in spaced relationship with the upper electrode I2. The resistor includes the rod of insulating material Il, around which is helically wound the resistance wire I8, the latter being connected at its respective ends to the conducting terminals 2i] and 2|. A coating I S, of vitreous enamel or other suitable heat-resistant insulating material, may be provided over the conductor I3. The lower terminal 2l of the resistor engages the lower conducting electrode I 3, and the upper terminal 20 is engaged by the intermediate electrode I6, the latter extending outwardly and laterally in threaded engagement through the wall of the inner tubular insulator II its outer end being exposed to the annular space I4 at a point spaced from both the upper electrode I2 and the lower electrode I3.

In accordance with common practice, a leakage-gap arrangement is provided at the upper end of the device, including the insulator 29, of ceramic material, in which the cemented insert 30 is arranged to cooperate with an externally tl'ireaded,upwardly extending portion of the upper electrode l2, the outwardly and upwardly extending lower leakage-gap electrode 3| being conveniently held in place by clamping a portion thereof between the insulator 2S and the upper electrode I2. At the upper end of the insulator 29 an upwardly extending threaded stud is secured in any suitable manner, and the upper leakage-gap electrode 32 arranged to extend toward and in spaced relation to the lower leakage-gap electrode 3i, the clamping nut 33, tting the stud 36, holding the electrode 32 in place. The device is shown connected to a line conductor 35, the latter being clamped between the nuts S3 and 34, both of which cooperate with the threads of the stud 36.

At the lower end of the device, the lower electrode I3 is provided with the centrally positioned, downwardly extending threaded portion 24, and

a mounting bracket 23 may be clamped between title lower surface of the lower electrode I3 and the nut 25, the latter engaging the threaded portion 2d. The lower electrode I3 is connected to the ground 28 by means of the grounding conductor 2l, one end of the latter being clamped between the terminal nut 26 and the clamping nut 25.

The material from which the insulators I and I I are constructed is one which evolves gases which are highly ionized and electrically conducting at or near atmospheric pressures in response to an arc, one such material being hard ber. The vent openings 22 of the lower electrode I3, in communication respectivelywith the annular space I4 and the outside of the outer tube, provide the only means of egress for the gases formed within the annular space.

From the arrangement above described, it will be apparent that the weakest initial or preferential arc path through the device is from the upper electrode 12 to the intennediate electrode I6, and thence through the resistor to the lower electrode I3. It will also be clear that any gases evolved as a result of an arc initiated between the electrodes I2 and I6 will move along the annular space I4 to the vents 22. These gases, being highly conducting, provide a gaseous conducting path electrically connecting the electrode I6 to the lower electrode I3, thereby shunt-circuiting the resistor.

'Ine current carrying capacity of the resistor should be such 'that 'it will carry lthe vsuperin'iposed current and the line-to-ground current available from the connected circuit without damage for i the short interval prior to initiation of the shunting arc between the electrodes I6 and I3, and the spacing and restriction of the arc path between the electrodes I2 and I6 such that circuit interruption vwill occur when the follow current is limited only by the resistor. If the lightning current is severe, 'that is, great in magnitude and/or duration, the gases due -only "to the vsurge current may cause the desired shunt-circuiting of the resistor, the device thus tending to be selfprotec'ting in that the elapsed time for initiating the shunting arc is decreased as the need for so doing is increased.

The sequence of events when discharging relatively large surge currents follows: (1) breakdown of leakage-gap `and preferential arc path from electrode I2 to electrode 16'; (2) passage of current from electrode I2 to `electrode IS and thence to ground through the resistor; (3) discharge of conducting gas from preferential ar'c path through the vents 22 to'electricaliy connect the electrode IB lto the electrode 13'; (4) continued discharge of surge current through the parallel arrangement of resistor and shunting gas path until reduced to substantially zero; and (5) extinguishment of the arc maintained by the follow current and limited by the resistor I8 at the first current zero by expulsion action occurring along the arc path between the electrodes I2 and I6. Certain `values of surge current may be too small to cause the .above-described shunting eifect, arc extinguishment in such cases being due simply to the effect of the resistor `I8 in limiting the follow current to a value readily extinguished by the expulsion action between the electrodes I2 'and I6. All of the above events occur with great rapidity, the entire sequence requiring a, maximum of 1/g cycle.

From the above description, it will be noted that I provide an organization in which the conducting gases inherently discharged from an eX- pulson chamber are utilized to establish a protective gaseous current-carrying path in shunt with the resistor, the conductivity of the path varying directly with the magnitude and duration of the current to be discharged or interrupted. The operation of the device therefore automatically adjusts itself to the imposed conditions, and the abrupt change resulting from the use of an open-air gap in shunt with the resistor is avoided.

The above description of the invention is intended to be illustrative, rather than limiting- I claim, as my invention:

l. A lightning arrester comprising two hollow tubularV insulators which differ in diameter, upper and lower normally insulated conducting electrodes associated with said insulators, means including said electrodes for supporting said insulators in coaxial spaced relationship one within the other to provide an annular space therebetween, means including a resistor supported with- 'in 'the hollow of the insulator of lesser diameter for providing a preferential arc path within said annular arc space, and means responsive to the occurrence of an arc over said path for yshuntcircuiting said resistor.

2. A lightning arrester comprising two hollow tubular insulators which diier in diameter, upper and lower normally insulated conducting electrodes associated with said insulators, means including said electrodes for supporting said insulators in coaxial spaced relationship one within the other to provide an annular space therebetween, means including a resistor supported Within theholl'ow of the insulator of lesser diameter for providing a preferential arc path within saidannular arc space, and means responsive to the occurrence of an arc over said preferential arc path for establishing a gaseous conducting arc ypath in shunt circuit relation with respect to said 'resistor and in series circuit relation with respect tosaid preferential arc nath.

3. A lightning arrester of the expulsion typ comprising two hollow tubular insulators of d-..- fering diameter, spaced/upper and lower conduct" ing electrodes vat the yrespective ends of said insulators, means including said electrodes for supporting said insulators in coaxial spaced relationship one within the other to provide a uniform 'longitudinally extending annular space therebetween, means including a resistor posi-- tioned within the hollow of the insulator cf lesser diameter for providing a preferential arc path within said annular' space, said resistor having its lower end electrically connected to and sul ported by the lower electrode and extending upwardly therefrom in normally insulated spaced relation wtih the upper electrode, and means responsive to the occurrence of an arc over said preferential arc path :for establishing a gaseous arc path within said annular space in shunt relation with said resistor, said last-named means including vent means for said annular space only in said lower electrode in kconnnunicaiion with the outside ofthe outer tube.

4. A lightning arrester of the expulsion type comprising two hollow tubular insulators oi differing diameter, spaced upper and lower conducting electrodes at the respective ends of said insulators, means including said electrodes [or supporting said insulators in Coaxial spaced relationship one within the other to provide a uniform longitudinally extending annular space therebetween, means including a resistor positioned within the hollow of the insulator of lesser diameter for providing a preferential arc path within said annular space, one end of said resistor engaging the lower electrode and extending upwardly therefrom in normally spaced insulated relation with the upper electrode, and vent means in said lower electrode for said annular arc space.

5. A lightning arrester of the expulsion type comprising two hollow tubular insulators of differing diameter, spaced upper and lower electrodes at the respectiveends of said insulators, means including said electrodes for supporting Vsaid insulators in coaxial spaced relationship one Within the other to provide a uniform longitudinally extending annular space therebetween, vent means in said lower electrode for communication respectively with said annular space and the outside of the outer tube, a resistor positioned Within the hollow of the insulator of lesser diameter, one end of said resistor engaging the lower electrode and extending upwardly therefrom in spaced relationship with the upper electrode, said resistor providing means for initiating a primary arc within said annular space in series circuit relation with said resistor, and means responsive to the initiation of said primary arc for initiating a secondary arc within said annular space in shunt with said resistor and in series circuit relation with said primary arc.

6. In a liglhtning arrester of the expulsion type, a tubular dielectric structure comprising two concentric hollow cylindrical tubes of gas-evolving wall-material, means for providing an annular space therebetween, 'said means including spaced normally insulated conducting electrodes at the respective ends of said insulators, means including a resistance member contained within the hollow of the insulator of lesser diameter for initiating a primary arc within said annular space and in series circuit relation with said resistance member, and means responsive to the evolution 'of electrically conducting gas attending said primary arc for providing a secondary arc within said annular space in shunt circuit relation with said resistance member and in series circuit relation with said prmary arc.

RALPH R. PITTMAN. 

